| Description |
The Lodore Formation, an Upper Cambrian transgressive sandstone, outcrops along the Uinta Mountain Uplift in northeast Utah and north-west Colorado. Sandstone in the Lodore Formation is multicyclic, moderately to well sorted, subrounded quartzarenite, subarkose and arkose. Orthoclase is the most abundant feldspar; sedimentary rock fragments the most common rock fragments. Matrix generally constitutes less than 12 percent of the rock, and rock fragments consitute less than 1 percent. Rounded ziron, tourmaline and rutile are the principal heavy minerals. Diagenesis has led primarily to silica cementation. Other minerals introduced during diagenesis include hematite, apatie and calcite, dolomite and gypsum cement. The Lodore Formation is dominated by sandstone, but siltstone, claystone, and, rarely, sandy glauconitic dolmite are present in the upper part of the formation in the Dinosaur National Monument area. The basal part of the formation is generally coarse-grained and feld-spathic. Sedimentary structures, grain size trends, occurrence of trace fossils and body fossils, and the overall paleogeographic setting show that the Lodore Formation was deposited in nearshore marine environments. Variations in these physical and biological structures allow the identification of the beach and tidal flat sub-environments of the nearshore marine setting of the Lodore Formation. Analysis of cross-stratification and petrographic examination indicate that the Lodor Formation was derived mainly from the Precambrian Uinta Mountain Group. The stratigraphy of the Lodore Formation is in need of revision. Information gathered in this study suggests that the formation is late Middle Cambrian to Late Cambrian in age. |
